Devices that consume electrical power are ubiquitous in today's society. Many of these devices rely on electrical power stored in batteries and other energy storage devices such as, for example, capacitors in order to operate, while others rely on a different type of electrical power, such as a wall outlet. For battery-powered devices, typically the batteries are charged when the device is not in use, and are at least partially discharged as the device is used, thereby consuming the electrical power from the battery. With the increasing importance of electronic devices, device manufacturers are striving to make devices and batteries that run more efficiently (e.g., devices that consume less power and batteries that last longer on a single charge and generate less waste heat) and have a longer useful lifetime. In order to improve the performance of electronic devices and batteries, it is useful to understand the operating characteristics, including the thermal operating characteristics, of the devices and the batteries in order to, for example, design thermal management systems and/or redesign the device or battery in order to improve performance.
Calorimeters have previously been used to measure thermal operating characteristics of small batteries (e.g., hearing aid batteries), with the thermal operating characteristics including, among other things, the heat generated when the batteries are charged and/or discharged. These calorimeters, however, are typically very small in size and therefore of limited usefulness for determining thermal operating characteristics of larger batteries or for measuring thermal operating characteristics of other types of electronic devices. Moreover, attempts at increasing the size of these relatively small calorimeters in order to test larger batteries and other kinds of electronic devices have had limited success.
Some of the batteries that are particularly difficult to test using conventional calorimeters are those batteries used in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), all-electric vehicles (EVs) and other kinds of electric vehicles. These batteries are typically very large, very heavy, and have very large current ratings. As HEVs, PHEVs, EVs, and other types of electric vehicles gain an increasing share of the global market for vehicles, automakers are developing more advanced vehicles and batteries that can operate efficiently and that can endure large numbers of charge and discharge cycles. This shift is spurred by a number of converging forces, such as state requirements for zero-emission vehicles, higher corporate average fuel economy standards, greenhouse gas regulations, the threat of oil price spikes, new smart grid and vehicle-to-grid technologies, and advances in battery technologies. The next generation of electrified cars and light trucks will aim to travel farther on electric power alone, placing greater power demands on the vehicles' battery packs. To meet these demands, automakers are building larger battery packs with advanced battery technologies, and are cycling batteries between greater states of charge. However, batteries typically generate waste heat as they are charged and discharged. This heat must be directed away from the battery through thermal control and/or management in order to prevent adverse effects on the life of the battery that comes from exposure to elevated temperature. The thermal management of these battery packs is thus very important to the life-cycle cost of the battery pack and efficient operation of the vehicle.
More generally speaking, understanding and controlling the thermal operating characteristics of a wide variety of electronic devices and batteries can be important in estimating and/or improving the performance and expected life of the devices and batteries. For example, the performance (e.g., instantaneous current capacity, total charge available, etc.), charge cycling and/or calendar life of a battery can significantly decline if the battery is not properly cooled, or if it is cycled too frequently or too rapidly. In the context of electric vehicles, reduced performance from the battery can lead to reduced gas mileage, and may lead to premature failure of the battery. As another example, for lithium-ion battery packs, overheating can lead to a fire or explosion of the battery pack. As still another example, some batteries may experience phase transitions during operation. These phase transitions may cause expansion and/or contraction of the constituent elements of the battery and may lead to cracks or other damage to the battery, which will reduce its life—a calorimeter can identify the battery operating point at which these phase transitions occur and a control system can be designed to avoid these operating points and extend the life of the battery.
If the thermal operating characteristics, such as, for example, the amount of heat generated during high current discharge, of an electronic device or battery are known, however, a manufacturer may be able to design an appropriate thermal management system to help mitigate performance losses and other problems that may otherwise be caused by, for example, a device or a battery overheating. The manufacturer may also be able to design improvements to the electronic device and/or battery.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.